A combine harvester comprises a threshing unit arranged to receive and thresh a crop stream. Separating apparatus are located downstream and rearward of the threshing unit and are arranged to receive the threshed crop stream and convey such a rearward direction. The front of a return pan, disposed below the separating apparatus, overlaps the rear of a stratification pan, disposed below the threshing unit. The stratification pan is driven in an oscillating manner to convey a primary grain/chaff stream rearwardly to a rear edge from where the primary grain/chaff stream falls under gravity into a cleaning unit. The return pan is driven in an oscillating manner to convey a secondary grain/chaff stream forwardly to a front edge from where the secondary grain/chaff stream falls under gravity to combine with the primary grain/chaff stream on the stratification pan. The cleaning unit comprises a fan for generating a cleaning airstream which is directed through the falling grain/chaff stream to encourage the lighter material away from the grain. A plurality of crop flow disrupting elements in the form of fins or tines are secured to the underside of the return pan above the stratification pan to disrupt the grain/chaff stream and enhance stratification thereof.